Most machine tools of this type comprise a numerical control, e.g., a NC control or a CNC control. The control data required for the numerical control, e.g., position and/or path or contour data for the desired workpiece machining, is fed to the control device in the form of control inputs and subsequently converted into control signals for the servo drives of the machine tool.
One example of such a machine tool is an electrical discharge machine, i.e., an erosive die sinking or erosive cutting machine. Such electrical discharge machines are used, among other purposes for the manufacture of stamps and/or dies of conductive materials. One advantage of such machines can be seen in the extremely high precision. One particularly economical utilization of such electrical discharge machines is the manufacture of tool molds for the mass production of tools. In this case, it the individual control data, i.e., only the control data for a given workpiece must be entered before the machining of one or more workpieces. In addition to the definition of the desired machining steps to be carried out on the workpiece, corresponding control data that describes the processing sequence of the respective machine must be entered for each machine type.
The initially mentioned control methods according to the state of the art require control inputs in the form of closed routine "programs" or so-called sequential control programs. Such a program comprises all control data and, for example, defines the quality, machine parameters, sequence, position on the workpiece to be machined, etc., of the cutting paths to be traveled. The control data is defined in the form of a sequence of commands. In this case, a command that corresponds to a certain machining step remains active until a new machining step in the command sequence of the control program is defined by a new command. The machining sequence is strictly defined for each individual type of machine tool. If an intentional or unintentional interruption of the machine occurs during the sequential machining of a workpiece, e.g., a defect that cannot be immediately repaired, the machine operator is forced to continue the machining on another machine. For this purpose, the machine operator must completely readjust the sequential control program, i.e., the operator must read in and start the control program. In addition, the machine operator may be required to adapt the control program to the new machine tool. The entire machining sequence is carried out again on the other machine, i.e., the same workpiece is passed through in quasi-idle fashion until the condition at the time of the interruption is reached. Consequently, the machine again travels along the entire contour, in certain instances even several times. In this case, it may occur that additional material is removed and the already machined surface is damaged. This represents a particularly critical aspect in erosive trimming processes. If a workpiece is, again clamped in another machine, for example, this risk becomes much higher. Although this risk can be partially eliminated by means of complicated aligning methods, damage to the workpiece surface while the machine again travels along the workpiece contour, e.g., when producing a cut with the wire electrode of an erosive cutting machine, cannot always be prevented. Under certain circumstances, it is more practical to use a new, unmachined workpiece and to remachine the entire workpiece. In this case, the originally machined workpiece is discarded as waste and lost.
In addition, machine tools represent relatively expensive systems, i.e., such machine tools should operate over 24-hour periods. Today, a variety of automatic feed devices is available for this purpose such that an arbitrary number of workpieces can be automatically processed if the machine operator is not present for extended periods of time. Consequently, the demands for flexibility of modern machine tools are very high. However, the machine operator or the production manager is essentially responsible for selecting a sensible machining sequence for the given orders so as to prevent bottlenecks during the processing of orders. In practical applications, it is, however, frequently required immediately to process an unexpected order that is extremely urgent. This means that it must be possible to move a workpiece to another fixture of the same machine or to another machine so as to process a special order.